1. Field of the Invention
The present invention relates to a resist process apparatus for performing a resist process of a semiconductor wafer and, more particularly, to a wafer holding mechanism for holding a semiconductor wafer.
2. Description of the Related Art
With an increase in packing density of semiconductor elements, a resist process of a semiconductor wafer is becoming more complicated. For this reason, a resist process apparatus includes a plurality of process mechanisms, such as a mechanism for processing a semiconductor wafer with hexamethyldisilazane (HMDS), a mechanism for coating a resist solution on the wafer, a mechanism for baking the wafer, and a mechanism for performing a developing treatment of the wafer.
In a conventional resist process apparatus, the respective process mechanisms (a plurality of resist coating mechanisms, baking mechanisms, and the like) are arranged in tandem between a loader mechanism and an unloader mechanism, and handling mechanisms for conveying wafers are between the respective process mechanisms. Since the process mechanisms are arranged in a line in this manner, the apparatus cannot respond to changes in process.
In order to eliminate the above-described drawback of the line type resist process apparatus, an improved resist process apparatus disclosed in U.S. application Ser. No. 320,619 and No. 357,279 is designed to have a flexible arrangement as a whole so as to respond to a complicated process or changes in process. In this improved resist process apparatus, a track is arranged, and a handling device is moved within this track so as to select a necessary mechanism from the respective process mechanisms such as coating and baking mechanisms.
The above handling device has a suction arm at a position where a semiconductor wafer is held. However, when a semiconductor wafer is held by suction by the suction arm, dust is accumulated near the suction port, and hence dust tends to adhere to the semiconductor wafer.
In addition, if a resist process apparatus has a complex mechanism, the amount of dust generated from the mechanism is increased, and the interior of a clean room becomes susceptible to contamination. As a result, dust tends to adhere to semiconductor wafers, and the ratio of non-defective semiconductor wafers may be decreased.
In order to eliminate the drawbacks of such a conventional handling device, U.S. Pat. No. 4,507,078 discloses a handling device for holding a semiconductor wafer by using a ring-like member. According to such a handling device, since a semiconductor wafer is held by simply fitting the wafer in the ring-like member, the amount of dust adhering to the semiconductor wafer is greatly decreased.
In the above-described handling device, however, since heat exchange is performed through a contact portion between a semiconductor wafer and the ring-like member, a difference in temperature between the peripheral and central portions of the semiconductor wafer is caused. This may adversely affect the subsequent processes. In a resist process apparatus, since the temperature of a semiconductor wafer varies in an HMDS treatment, resist coating, a developing treatment, and the like, the wafer temperature is adjusted in a pre-process of each treatment. However, since a target temperature in each process may differ from an actual wafer temperature, the wafer temperature in a resist process cannot be accurately managed, thus posing various problems. For example, the thickness of a resist film fails to reach a target thickness.